A study of the capacity fade of a LiCoO2/graphite battery during the temperature storage process at 45 °C under different SOCs.

Lithium-ion batteries with lithium cobalt oxide (LiCoO2) as a cathode and graphite as an anode are promising energy storage systems. However, the high-temperature storage mechanism under different states of charge (SOCs) conditions in batteries remains inadequately elucidated, and a clear storage policy has yet to be established. This study investigates and compares the capacity decay mechanism of a 63 mA h LiCoO2/graphite battery at 45 °C under various SOCs (100%, 75%, 50%, 30%, 0%), while also analysing the underlying reasons for this decay. The exhibited capacity recovery rates under 30% SOC and 100% SOC were significantly higher compared with those of the 50% and 75% SOC levels. Additionally, an analysis was conducted on battery storage under 0% SOC conditions, revealing its unsuitability for storage. By disassembling and analysing the batteries after storage, it was found that the dead lithium (Li) and cobalt (Co) in the anode gradually increased with the extension of storage time when stored under the same SOC. Finally, storage schemes under different SOCs are proposed, providing valuable suggestions for battery storage.

Harmless pre-lithiation via advantageous surface reconstruction in sacrificial cathode additives for lithium-ion batteries.

Sacrificial cathode additives have emerged as a tempting strategy to compensate the initial capacity loss (ICL) in Li-ion batteries (LIBs) manufacturing. However, the utilization of sacrificial cathode additives inevitably brings residuals, side reactions, and negative impacts in which relevant researches are still in the early stage. In this study, we conduct a systematic investigation on the effects of employing a nickel-based sacrificial additive, Li2Cu0.1Ni0.9O2 (LCNO), and propose a feasible strategy to achieve advantageous surface reconstruction on LCNO. Specifically, we build a Li5AlO4 (LAO) coating layer on the LCNO through dry ball milling and annealing treatment. This process not only consumes surface residual lithium compounds on LCNO but also demonstrates minimal detrimental effects on its performance. The surface reconstructed LCNO (SR-LCNO) reveals mitigated gas generation and suppressed structure degradation under high working voltage (＞4.1 V), thereby causing negligible negative effects on the cycling capability and rate performance of commercial cathode materials. The full cells containing SR-LCNO deliver significantly improved electrochemical properties, with no observed exacerbation of side reactions. This work awakes the awareness of the prudent utilization of sacrificial cathode additives and provides an effective strategy for harmless pre-lithiation via surface reconstructed sacrificial cathode additives.

Direct Observation of the Evolutionary Process in Room-Temperature Sodium-Sulfur/Selenium Batteries Using operando Light Microscopy.

Understanding the conversion mechanism of active materials in the electrode is essential to guide the design of room-temperature sodium-sulfur/selenium (RT Na-S/Se) batteries. However, there is still some confusion regarding the dissolution and formation of the insulating active particles. Conventional detection methods have difficulty in capturing and presenting the dynamic processes of these microscopic particles in the "black box" battery. In this study, a visualization technique was applied to track and monitor the internal evolution process of RT Na-S/Se batteries, visualizing the dissolution and formation details of insulating solid particles in real time. Supercooled liquid sulfur and spherulites were also observed for the first time in this system. The microstructural evolution mechanism is inferred based on the observation of the dynamic information on microscopic particles. This paper provides insights into the internal workings of RT Na-S and Na-Se batteries, allowing for a more comprehensive and in-depth understanding of their dynamics.

Rational design of intergrowth P2/O3 biphasic layered structure with reversible anionic redox chemistry and structural evolution for Na-ions batteries.

Layered oxides have attracted unprecedented attention for their outstanding performance in sodium-ion battery cathodes. Among them, the two typical candidates P2 and O3 type materials generally demonstrate large diversities in specific capacity and cycling endurance with their advantages. Thus, composite materials that contain both P2 and O3 have been widely designed and constructed. Nevertheless, the anionic/cationic ions' behavior and structural evolution in such complex structures remain unclear. In this study, a deep analysis of an advanced Na0.732Ni0.273Mg0.096Mn0.63O2 material that contains 78.39 wt% P2 phase and 21.61 wt% O3 phase is performed based on two typical cathodes P2 Na0.67Ni0.33Mn0.67O2 and O3 NaNi0.5Mn0.5O2 that have the same elemental constitution but different crystal structures. Structural analysis and density functional theory (DFT) calculations suggest that the composite is preferred to form a symbiotic structure at the atomic level, and the complex lattice texture of the biphase structure can block unfavorable ion and oxygen migration in the electrode process. Consequently, the biphase structure has significantly improved the electrochemical performance and kept preferable anionic oxygen redox reversibility. Furthermore, the hetero-epitaxy-like structure of the intergrowth of P2 and O3 structures share multi-phase boundaries, where the inconsistency in electrochemical behavior between P2 and O3 phases leads to an interlocking effect to prevent severe structural collapse and relieves the lattice strain from Na+ de/intercalation. Hence, the symbiotic P2/O3 composite materials exhibited a preferable capacity and cyclability (∼130 mAh g-1 at 0.1 C, 73.1% capacity retention after 200 cycles at 1 C), as well as reversible structural evolution. These findings confirmed the advantages of using the bi/multi-phase cathode for high-energy Na-ion batteries.

Stabilization of Multicationic Redox Chemistry in Polyanionic Cathode by Increasing Entropy.

Polyanionic compounds have large compositional flexibility, which creates a growing interest in exploring the property limits of electrode materials of rechargeable batteries. The realization of multisodium storage in the polyanionic electrodes can significantly improve capacity of the materials, but it often causes irreversible capacity loss and crystal phase evolution, especially under high-voltage operation, which remain important challenges for their application. Herein, it is shown that the multisodium storage in the polyanionic cathode can be enhanced and stabilized by increasing the entropy of the polyanionic host structure. The obtained polyanionic Na3.4 Fe0.4 Mn0.4 V0.4 Cr0.4 Ti0.4 (PO4 )3 cathode exhibits multicationic redox property to achieve high capacity with good reversibility under the high voltage of 4.5 V (vs Na/Na+ ). Exploring the underlying mechanism through operando characterizations, a stable trigonal phase with reduced volume change during the multisodium storage process is disclosed. Besides, the enhanced performance of the HE material also derives from the synergistic effect of the diverse TM species with suitable molarity. These results reveal the effectiveness of high-entropy concept in expediting high-performance polyanionic cathodes discovery.

Heteroatom-Substituted P2-Na2/3Ni1/4Mg1/12Mn2/3O2 Cathode with {010} Exposing Facets Boost Anionic Activity and High-Rate Performance for Na-Ion Batteries.

As an attractive cathode candidate for sodium-ion batteries, P2-type Na2/3Ni1/3Mn2/3O2 is famous for its high stability in humid air, attractive capacity, and high operating voltage. However, the low Na+ transport kinetics, oxygen-redox reactions, and irreversible structural evolution at high-voltage areas hinder its practical application. Herein, a comprehensive study of a microbar P2-type Ni2/3Ni1/4Mg1/12Mn2/3O2 material with {010} facets is presented, which exhibits high reversibility of structural evolution and anionic redox activity, leading to outstanding rate capability and cyclability. The notable rate performance (53 mA h g-1 at 20 C, 2.0-4.3 V) contributed to the high exposure of {010} facets via controlling the growth orientation of the precursor, which is certified by density functional theory calculation and lattice structural analysis. Mg substitution strengthens the reversibility of anionic oxygen redox and structural evolution in high-voltage areas that was confirmed by the in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy tests, leading to outstanding cyclic reversibility (68.9% after 1000 cycles at 5 C) and slowing down the voltage fading. This work provides new insights into constructing electrochemically active planes combined with heteroatom substitution to improve the Na+ transport kinetics and structural stability of layered oxide cathodes for sodium storage.

Boosting potassium-storage performance via confining highly dispersed molybdenum dioxide nanoparticles within N-doped porous carbon nano-octahedrons.

The development of durable and stable metal oxide anodes for potassium ion batteries (PIBs) has been hampered by poor electrochemical performance and ambiguous reaction mechanisms. Herein, we design and fabricate molybdenum dioxide (MoO2)@N-doped porous carbon (NPC) nano-octahedrons through metal-organic frameworks derived strategy for PIBs with MoO2 nanoparticles confined within NPC nano-octahedrons. Benefiting from the synergistic effect of nanoparticle level of MoO2 and N-doped carbon porous nano-octahedrons, the MoO2@NPC electrode exhibits superior electron/ion transport kinetics, excellent structural integrity, and impressive potassium-ion storage performance with enhanced cyclic stability and high-rate capability. The density functional theory calculations and experiment test proved that MoO2@NPC has a higher affinity of potassium and higher conductivity than MoO2 and N-doped carbon electrodes. Kinetics analysis revealed that surface pseudocapacitive contributions are greatly enhanced for MoO2@NPC nano-octahedrons. In-situ and ex-situ analysis confirmed an intercalation reaction mechanism of MoO2@NPC for potassium ion storage. Furthermore, the assembled MoO2@NPC//perylenetetracarboxylic dianhydride (PTCDA) full cell exhibits good cycling stability with 72.6 mAh g-1 retained at 100 mA g-1 over 200 cycles. Therefore, this work present here not only evidences an effective and viable structural engineering strategy for enhancing the electrochemical behavior of MoO2 material in PIBs, but also gives a comprehensive insight of kinetic and mechanism for potassium ion interaction with metal oxide.

An advanced BiPO4/super P anode material for high-performance potassium-ion batteries.

Dispersed BiPO4 nanoparticles loaded on the surface of a super P conducting network (BiPO4/SP) were fabricated and investigated as a novel anode for PIBs. The BiPO4/SP electrode demonstrates high rate capability (97.1 mA h g-1 at 500 mA g-1) and good long-term cycling performance (116 mA h g-1 at 200 mA g-1 over 100 cycles).

Enhanced Activity and Reversibility of Anionic Redox by Tuning Lithium Vacancies in Li-Rich Cathode Materials.

Li-rich Mn-based layered oxide cathodes (LLOs) are considered to be the most promising cathode candidates for lithium-ion batteries owing to their high-voltage platform and ultrahigh specific capacity originating from anionic redox. However, anionic redox results in many problems including irreversible oxygen release, voltage hysteresis, and so on. Although many efforts have been made to regulate anionic redox, a fundamental issue, the effect of lithium vacancies on anionic redox, is still unclear. Herein, we synthesized a series of LLO materials with different lithium vacancy contents by controlling the amount of lithium salt. Specifically, lithium-vacancy-type LLOs Li1.11Ni0.18Co0.18Mn0.53O2 with a pompon morphology exhibit an ultrahigh specific capacity (293.9 mA h g-1 at 0.1 C), an outstanding long-term cycling stability (173.5 mA h g-1 after 300 cycles at 1 C), and an excellent rate performance (106 mA h g-1 at 10 C). It reveals that lithium vacancy is a key factor to enhance anionic redox activity and reversibility. Lithium vacancies exhibit different inductive effects on the structure of the surface and bulk. Abundant surface oxygen vacancies and a surface spinel phase layer induced by lithium vacancies suppress irreversible oxygen release, while the bulk phase transformation and cation disorder combined with sufficient lithium vacancies in the bulk stabilize structure and improve anionic redox kinetic. The findings offer a significant theoretical guidance for the practical application of LLO materials.

Stabilizing Na metal anode with NaF interface on spent cathode carbon from aluminum electrolysis.

We report the synthesis of spent cathode carbon (SCC) with a NaF interface from aluminum electrolysis, and its application as a Na metal anode host. The SCC anode exhibits superior ion conductivity and a high shear modulus. The natural NaF interface on the SCC anode can regulate Na+ transmission and inhibit dendrite growth. Furthermore, the anode can be used to turn waste into treasure through directly using spent cathodic carbon without any chemical processing. The green SCC electrode exhibits a higher flat voltage and better reversibility compared with purified cathode carbon without NaF.

Encapsulating V2O3 Nanoparticles in Hierarchical Porous Carbon Nanosheets via C-O-V Bonds for Fast and Durable Potassium-Ion Storage.

Vanadium oxide (V2O3) has been considered as a promising anode material for potassium-ion batteries (PIBs), but challenging as well for the low electron/ion conductivity and poor structural stability. To tackle these issues, herein, a novel sheetlike hybrid nanoarchitecture constructed by uniformly encapsulating V2O3 nanoparticles in amorphous carbon nanosheets (V2O3@C) with the generation of C-O-V bonding is presented. Such a subtle architecture effectively facilitates the infiltration of electrolyte, relieves the mechanical strain, and reduces the potassium-ion diffusion distance during the repetitive charging/discharging processes. The generated C-O-V bonding not only accelerated charge transfer across the carbon-V2O3 interface but also strengthened the structural stability. Benefiting from the synergistic effects, the as-prepared V2O3@C nanosheets display fast and durable potassium storage behaviors with a reversible capacity of 116.6 mAh g-1 delivered at 5 A g-1, and a specific capacity of 147.9 mAh g-1 retained after 1800 cycles at a high current density of 2 A g-1. Moreover, the insertion/extraction mechanism of V2O3@C nanosheets in potassium-ion storage is systematically demonstrated by electrochemical analysis and ex situ technologies. This study will shed light on the fabricating of other metal oxides anodes for high-performance PIBs and beyond.

Engineering 3D Well-Interconnected Na4MnV(PO4)3 Facilitates Ultrafast and Ultrastable Sodium Storage.

Na4MnV(PO4)3 (denoted as NMVP) has drawn increasing attention owing to the three-dimensional framework and high theoretical capacity. Nevertheless, the inherent low electronic conductivity of NMVP impedes the scale-up commercial applications. In this work, the feasibility to achieve ultrahigh-rate capability and long lifespan by in situ embedding the intertwined carbon nanotube (CNT) matrix into the bulk of Na4MnV(PO4)3@C composites through a facile wet-chemical approach is reported. The elaborately prepared Na4MnV(PO4)3@C@CNTs cathode delivers a discharge capacity of 109.9 mA h g-1 at C/5 with an impressive rate capability of 68.9 mA h g-1 at an ultrahigh current rate of 90 C as well as a fascinating cycling performance of 68.3% capacity retention at 40 C after 4000 cycles. The optimum design of the 3D well-interconnected NMVP permitting fast kinetics for transported Na+/e- is beneficial to the excellent electrochemical performance, which is further studied by the galvanostatic intermittent titration technique, cyclic voltammetry, and electrochemical impedance spectra measurements. The pseudocapacitance contributions are also investigated. The research demonstrates that the dual-nanocarbon synergistically modified NMVP composite is expected to facilitate the commercialization of sodium-ion batteries.